The use of laser energy for modification of material surfaces is now plausible in dentistry due to the advent of fiber optic delivery systems and short pulse durations. Dentin, the primary component of tooth structure, is the principal determinant of most operations in restorative dentistry. Currently, bonding techniques to dentin do not approach the success of bonding to enamel and failure of the bond results. The objective of this proposal is to conduct a systematic, detailed investigation into the effect of pulsed infrared lasers on dentin to improve the performance of restorations bonded to dentin. The central hypothesis is that the dentin surface can be structurally and chemically modified using pulsed infrared laser energy to improve the clinical success of the restorative procedure without detrimental pulpal effects. Specific aims are: 1. to determine the optical properties of sound and carious dentin in the infrared region of the electromagnetic spectrum, 2. to identify the chemical composition of the laser-modified dentin surface using Energy Dispersive Spectroscopy (EDS), and Fourier Transform Infrared Spectroscopy (FTIR), and morphological changes with Scanning Electron Microscopy (SEM), 3. to use laser treatment of dentin surfaces to remove caries, enhance microhardness, bond strength, decrease permeability, and provide for caries inhibition, 4. to measure the pulpal temperature change from laser treatment in vitro and define clinical laser parameters which are atraumatic to pulpal tissue. 5. to test the efficacy of laser treatments in the clinical setting, including laser modification of dentin for restorative procedures and treatment of root surface hypersensitivity. The optical properties of dentin will define requirements for new laser systems with selective absorbance for diseased dentin. Identification of the chemical composition and morphological changes, in the laser treated dentin will permit development of new bonding strategies. The central hypothesis will be tested by repeated measures and multifactor randomized experimental design. Methods will include standard material testing and analytical techniques. In vivo experimentation will determine the safety and efficacy of laser modification of dentin surfaces. The clinical ramifications of this work will be to advance restorative dentistry by augmenting treatments of coronal and root caries, and root surface hypersensitivity.